A 27-year-old woman who was sentenced to death in Sudan last month for converting to Christianity from Islam has been freed after what the government said was "unprecedented" international pressure.

Mariam Yahya Ibrahim, who is married to a Christian American, was ordered by a Sudanese court last month to return to Islam and was sentenced to 100 lashes and to death.

Her release is likely to be welcomed by human rights groups and Western governments who voiced outrage at the ruling.

Britain had last month summoned the Sudanese charge d'affaires in protest at the sentencing.

"The appeal court ordered the release of Mariam Yahya and the cancellation of the (previous) court ruling," Sudan's SUNA news agency said.

A government official had told Reuters on 31 May that Sudanese officials were working to release Ms Ibrahim.

Ms Ibrahim was sent to a secret location for her protection, her lawyer said.

"Her family had been threatened before and we are worried that someone might try to harm her," the lawyer, Mohaned Mostafa, said.

Ms Ibrahim gave birth in prison to a daughter, her second child by her husband Daniel Wani, whom she married in 2011.

Sudan's Foreign Ministry said it had come under "unprecedented" international pressure to free her.

"Now that the independent Sudanese judiciary has said its word in the case of a single national, the Foreign Ministry would like to remind the international community about the continued suffering of 35 million nationals as a result of sanctions," its statement said.

The United States imposed sanctions on Sudan in 1997 over alleged human rights violations and support for what it called "international terrorism", then strengthened the penalties in 2006 over Khartoum's conflict with rebels in Darfur.  

State Department spokeswoman Marie Harf said: "As you know, the case has drawn the attention of the world, has been of deep concern to United States government and to many Americans."

She called on the government "to repeal its laws that are inconsistent with its 2005 interim constitution, the Universal Declaration of Human Rights and the International Covenant on Civil and Political Rights".

She added: "These actions would help demonstrate to the Sudanese people that their government intends to respect their fundamental freedoms and universal human rights."

Born to a Muslim father and an Ethiopian Orthodox Christian mother, Ms Ibrahim was convicted under Islamic sharia law that has been in force in Sudan since 1983.

The international outcry over her sentence included almost one million people who appealed to save her life on the Change.org petition website.